(I am exploring the costs and feasibility of a massively parallel hobbyist design project using a huge number of PICs on separate boards. I'll go into more detail later. For now I'm just trying to break this up into smaller questions.)

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Is there a printed circuit board fabrication manufacturing cost difference, between using all-SMT vs through-hole components, for simple board designs?

It seems that if you could make a simple single-layer PCB with no through-hole components, you could possibly save money due for no need for hole drilling or through-hole plating.

Or do board fabricators generally consider the cost of hole drilling and plating to be unimportant, and this is not usually factored into their board fab pricing?

I recognize that mechanical strength of the connections is reduced by not using through-hole mounting.

Most PCB manufacturers charge by the amount of copper they would have to use to make the boards and the board thickness..... and generally they do add charges for holes (through hole mounting pads and via's), this is usually included in the setup fee per order.

Good luck making a SMT board for anything even remotely complicated without vias...

Its not the fabricated board cost that will be the expense.. Its the cost of labor to populate an SMT vs through hole board.. In any decent volume SMT is hands down cheaper because its all done on a pick/place machine and run right through a reflow oven and done..